Cadmium-containing solders

Other criteria may be used to distinguish ancient from modem cadmium-containing solders. These criteria include... 

Other cadmium sources can include solder, galvanized pipes and metal fittings, pollution from disposal of cadmium-containing materials and from mining operations (see Chapter 7). However, concentrations of cadmium in drinking-water above the guideline value are unusual. 

Inhalation (breathing) When cadmium is scattered in the air as dust or fume, it can be inhaled and enter the upper respiratory tract and lungs. Operations that generate cadmium dust and fumes include welding with cadmium solder, or heating cadmium-containing compounds. Use a respirator to protect from this hazard. 

Table 9.2 shows the compositions and melting ranges of three 18 kt cadmium-free solder alloys and two containing cadmium compared with the solidification range for a typical 18 kt yellow gold casting alloy. 

The presence of the so-called heavy metals, eg, lead, cadmium, and antimony, iu traditional solders has become an important environmental issue owiag to concerns for health and safety. As a result, solders containing no lead and antimony such as tin—silver are finding a growing number of apphcations (Table 2). 

For soldering aluminum, combinations of cadmium and zinc are widely used, the most satisfactory being the 60% Cd—40% Zn alloy, in addition to a 95% Cd—5% Ag solder. In high speed and high temperature appHcations, which are too severe for tin or lead bearings, SAE 18, containing 1% nickel and 99% cadmium, and SAE 180, containing 0.7% silver, 0.6% copper, and 98.7% cadmium, are employed. 

Solders. Modem dental solders are made from mostly corrosion-resistant, nontoxic metals. Minimal quantities of tin and other elements are often added, some of which could produce toxic effects in the unalloyed state. Each solder is used for specific appHcations (180—188) typical compositions and properties of solders used in dentistry are presented in Table 11. Most of the ingredients of solders are resistant to corrosion, and alloying them with other ingredients renders the alloy safe for use in appHances placed in the oral environment. Silver solders corrode, but are used only for temporary appHances. Available products do not contain cadmium, although cadmium was an ingredient of some silver solders up to ca 1980. 

Silver-brazed joints are used when temperature or the combination of temperature and pressure is beyond the range of soldered joints. They are also more reliable in the event of plant fires and are more resistant to vibration. If they are used for fluids that are flammable, toxic, or damaging to human tissue, appropriate safeguarding is required by the code. There are OSHA regulations governing the use of silver brazing alloys containing cadmium and other toxic materials. 

Joining silver pieces with silver solder requires temperatures of 316-760°C. At these temperatures, impurities in the silver solder, such as antimony and cadmium, are released. The flux may contain fluoride compounds, such as potassium fluoride and boron trifluoride, or other boron compounds. 

Preparations containing cadmium (alloys) and intended to be used for brazing or soldering... 

---